PHP警告：mysqli_num_rows（）期望参数1为mysqli_result，boolean给出[duplicate]

I am a newbie PHP Developer and I'm trying to study how to create a simple login before I forego with the ones with session and cookies

My first code works but I want to lessen the code a bit, So i tried something else and this error appears and I'm curious why the other code doesn't work whereas they don't seem to be that different

    <?php
//The code that works
include("connection.php");

$connection = mysqli_connect(Server,Uid,Pwd,Database);
if(!$connection){
    die("Connection failed!" . mysqli_error($connection));
}

if(isset($_POST['submit'])){
    $username = mysqli_real_escape_string($connection,$_POST['username']);
    $password = mysqli_real_escape_string($connection,$_POST['password']);
     //$query = "SELECT * FROM 'user' WHERE Username = $username AND Password = $password";
     $query = "SELECT * FROM user WHERE  Username= '". mysqli_real_escape_string($connection,$username) ."' AND Password = '". mysqli_real_escape_string($connection,$password) ."'" ;
     $result = mysqli_query($connection,$query);
     $count = mysqli_num_rows($result);
     if ($count == 1){
        echo "Logged In Successfully! "; 
      }
       else{
        echo "Log In Failed! Invalid Username or Password! "; 
      }
}

?>



 <?php
//The code that doesn't work
include("connection.php");

$connection = mysqli_connect(Server,Uid,Pwd,Database);
if(!$connection){
    die("Connection failed!" . mysqli_error($connection));
}

if(isset($_POST['submit'])){
    $username = mysqli_real_escape_string($connection,$_POST['username']);
    $password = mysqli_real_escape_string($connection,$_POST['password']);
     $query = "SELECT * FROM 'user' WHERE Username = $username AND Password = $password";
     $result = mysqli_query($connection,$query);
     $count = mysqli_num_rows($result);
     if ($count == 1){
        echo "Logged In Successfully! "; 
      }
       else{
        echo "Log In Failed! Invalid Username or Password! "; 
      }
}

?>

Shouldn't they be just the same because in the second version of the code I just placed the mysqli_real_escape_string in the value of the variable so how come calling the $username and $password variable containing mysqli_real_escape_string produces this error? So does it always have to be like this every query?

</div>

1) Change SELECT * FROM 'user'.. to SELECT * FROM user... Single quotes are not allowed to enclose table or column name. Instead, Use Backtick.

2) Use PHP Prepared Statements

3) If storing plain password in DB, then encrypt it before saving it to table.

<?php
include("connection.php");

$connection = mysqli_connect(Server, Uid, Pwd, Database);
if (!$connection) {
  die("Connection failed!" . mysqli_error($connection));
}

if (isset($_POST['submit'])) {
  $stmt = mysqli_prepare($connection, "SELECT * FROM `user` WHERE Username = ? AND Password = ?");
  mysqli_stmt_bind_param($stmt, "ss", $_POST['username'], $_POST['password']);
  mysqli_stmt_execute($stmt);
  mysqli_stmt_store_result($stmt);
  $count = mysqli_stmt_num_rows($stmt);
  if ($count == 1) {
    echo "Logged In Successfully! ";
  } else {
    echo "Log In Failed! Invalid Username or Password! ";
  }
}
?>